A growing number of Pentagon officials and senior American military commanders are also voicing exasperation over a conflict that has spiraled into one of the world’s worst humanitarian disasters.

“There’s a level of frustration we need to acknowledge,” Lt. Gen. Jeffrey L. Harrigian, said in an interview in late August.

For all the turbulence, defenders of Saudi Arabia say, Prince Mohammed has proved himself a valuable ally for the United States.

“It’s been a rocky road, P.R. wise, but they made the right call, strategically,” said Ali Shihabi, the founder of the Arabia Foundation, who has close ties to the Saudi royal court. “They have an ally who is on the same page as they are.”

Still, the growing criticism from all quarters complicates those shared goals.

“Although from a distance the U.S.-Saudi relationship appears rock solid, there are cracks in the foundation,” said Robert Malley, a former White House coordinator for the Middle East, North Africa and the Gulf during the Obama administration.

“If one adds what happened to Jamal Khashoggi, and if some of the horrifying stories turn out to be true, one can imagine this having profound implications for U.S.-Saudi relations,” Mr. Malley said.